Pollution of marine environments near human population centers can expose marine mammals to carcinogenic and mutagenic chemicals. Humans residing near these areas may share some of the same food sources, exposing them to similar risks. We propose to adapt an established method for monitoring human populations for mutagen exposure, the autoradiographic hprt mutant lymphocyte assay, for use with California sea lions (Zalophus californianus). Assay conditions and baseline mutant frequencies will be established with blood samples obtained from a captive population at Sea World, San Antonio, Tx. As a "positive" control, lymphocytes from this population will be exposed to a reactive polyaromatic hydrocarbon, such as a benz(a)pyrene diol - epoxide, in vitro to determine their sensitivity to a characteristic environmental mutagen. Human lymphocytes will also be treated in vitro for comparison. Blood samples from 15-20 stranded free- living sea lions will be obtained from the Marine Mammal Center in Sausalito, CA. Lymphocytes will be assayed for frequencies of hprt mutants. Data on tissue levels of polycyclic aromatic hydrocarbons and organochlorine levels, as determined by the Marine Mammal Center, will be used to analyze the relationship between mutant frequency and exposure.